PETCT

PETCT, or PET/CT, is a hybrid medical imaging modality that combines positron emission tomography (PET) with computed tomography (CT) in a single examination. The fusion of metabolic information from PET with anatomical detail from CT improves lesion detection and localization compared with either modality alone.

In a typical PET/CT study, a radioactive tracer, most commonly fluorine-18 labeled fluorodeoxyglucose (18F-FDG), is injected intravenously. After a standard uptake period, the patient undergoes a PET scan to visualize tracer distribution, while a CT scan provides detailed body anatomy. The data are registered to produce fused images.

PET/CT uses various radiotracers beyond 18F-FDG for specialized indications. Tracers include 68Ga-labeled peptides for neuroendocrine tumors, amyloid or tau tracers for some neurodegenerative diseases, and other agents targeting cellular processes such as proliferation or hypoxia. Quantification with standardized uptake value (SUV) supports assessment of tracer activity.

Clinical uses span oncology, cardiology, and neurology. In cancer, PET/CT aids in detecting tumors, staging disease, guiding biopsy, monitoring treatment response, and detecting recurrence. In cardiology, it helps assess myocardial viability and inflammatory conditions. In neurology, it assists in evaluating dementia syndromes, epilepsy focus, and certain infections or inflammatory processes.

Limitations and safety considerations include ionizing radiation exposure to patient and staff, relatively high cost, and limited availability in some settings. False positives and negatives can occur due to inflammatory processes, recent procedures, hyperglycemia, or low tracer uptake. Preparation typically involves fasting and avoiding strenuous activity prior to the scan.

PET/CT emerged from the combination of PET and CT technologies in the late 1990s and early 2000s and has since become a widely used diagnostic tool. Variants such as PET/MRI are used in research and select clinical contexts.